Verification & changes
How the calculators are checked, what they do not cover, and every correction that changed a published result.
How results are checked
- Formulas and tables from the standard. Each calculator names the standard it follows. Table values, such as IEC 60364-5-52 current ratings or NEC 310.16 ampacities, are entered from the standard and checked against it.
- Hand calculations. For each calculator, at least one case is worked by hand and compared with the tool's result. Many of these are published as worked examples.
- Automated regression tests. 782 checks compare calculator results with the hand-calculated and tabulated values. Worked-example results are included, so a change that alters a published number makes a test fail. The suite runs before every update is published.
- Periodic review. The calculators and their wording are re-reviewed periodically. Confirmed errors are corrected, a test is added for each, and the change is logged below.
Known limitations
- The tools are for preliminary design and checking. Final designs should follow the project's own standards and be reviewed by a qualified engineer.
- IEC 60364-5-52 tabulates methods A1, B1, B2, C and D1 only up to 300 mm². Larger sizes are shown as unavailable for those methods rather than extrapolated.
- The resistance and reactance per metre used for voltage drop are typical published values. IEC 60364-5-52 does not tabulate them, so manufacturer data should be used where it differs.
- Arc-flash results follow IEEE 1584-2018 within its stated range (208 V to 15 kV, with its limits on gap and fault current).
- Cable pulling assumes identical round cables and a uniform friction coefficient along the route. Maximum tension and sidewall pressure limits should come from the cable manufacturer.
- Where a figure is an engineering rule of thumb rather than a value from a standard, the calculator says so on the page.
Change log
Corrections and additions that changed a calculated result or published content, newest first.
November 2026
Earth electrode formulas checked against BS 7430:2011+A1:2015
- Strip electrode (Earthing Grid Design): now uses BS 7430 9.5.5, R = ρ/(2πL)·ln(L²/(1.36·h·w)). The previous formula read about 10% low (12.1 Ω instead of 13.5 Ω for the default 10 m strip).
- Ring electrode (Earthing Grid Design and Ground Ring Resistance): BS 7430 gives no ring formula, so the pages no longer cite it. The ring-of-wire formula of IEEE Std 142 (Dwight) is now used. The previous formula read about 10% low (5.67 Ω instead of 6.33 Ω for the default ring), lower even than a straight wire of the same length.
- Rod and plate formulas confirmed against BS 7430 9.5.3 and 9.5.2. Added a worked example for a perimeter ring electrode.
November 2026
Worked examples, reference tables, report details, share links and unit toggles
- Nine new worked examples: motor run-up time, soft starter derating, MPPT charge controller, inverter DC:AC ratio, wind turbine output, solar tilt angle, switchgear short-circuit rating, NEC 25-ft tap rule and transfer switch sizing. Each result is pinned by a test.
- Reference tables under calculators (voltage drop mV/A/m, ambient and grouping factors, k values, transformer full-load and fault currents, standard device ratings, air density, soil resistivity), generated from the same data the calculators use.
- PDF reports can carry project, client, document reference, revision, prepared-by and checked-by fields, and now include the report title block.
- Share inputs: a link that reopens a calculator with the same inputs.
- Length, temperature and power fields can be switched between m/ft, °C/°F and kW/hp.
November 2026
Protection, IEC 61850 and EV checks
- Protection Coordination Workbench: the UK rule for 30 mA additional protection now follows BS 7671:2018+A2:2022 (socket-outlets up to 32 A). The previous 20 A limit came from the superseded 2008 edition and could miss 25 A and 32 A socket circuits.
- Settings philosophy sweep: rules with no data are shown as "not assessed", and the summary states that the assessment is incomplete, so a pass covers only the checks actually run.
- IEC 61850 SCL editor and guide: Type 1A GOOSE APPIDs (0x8000–0xBFFF) and Type 1A sampled-value APPIDs (0xC000–0xFFFF) are now recognised instead of being flagged. The report troubleshooting text now covers runtime reservation, enabling, data sets and trigger options.
- EV Charging: the cable is now sized so its rating covers the selected breaker (Ib ≤ In ≤ Iz), not just the design current. A list beside the result shows which checks are and are not performed.
- CT knee-point conversions are described as conventions (about 80 % or 1/1.2), not as exact relationships.
- Added two IEC 61850 worked examples (duplicate GOOSE addresses; tracing an unresolved GOOSE subscription), site search, and a Terms of use & disclaimer page.
November 2026
Installation method B2 and multi-cable pulling
- LV Cable Sizing, EV Charging, Solar PV and BESS: installation method B1 is now correctly described as insulated conductors or single-core cables in conduit on a wall. Method B2 (multicore cable in conduit on a wall) has been added from IEC 60364-5-52 Tables B.52.4 and B.52.5. Previously a multicore cable in conduit could only be modelled as B1, which overstates its current rating by up to about 16%.
- Cable Pulling Tension: added one cable, three cables triangular and three cables cradled. The weight correction factor is now applied to straight sections and bends, and sidewall pressure uses the formula for each configuration. For three cables this raises the calculated tension; in the worked example it rises from 200 lbf to 363 lbf.
- The cable-pulling worked example now states the number of cables, the weight of each cable and the total, and the configuration.
November 2026
Second technical review
- VFD energy savings: the affinity-law result is described as an upper bound on savings, not a conservative estimate.
- CT sizing: the fault-current table no longer extends beyond the CT's actual accuracy limit factor.
- Intrinsic safety, NFPA 110 and catalog descriptions: wording corrected to match the standards.
- Added a Short Circuit & Arc Flash guide, six worked examples and written guides under six more calculators.
October 2026
Full accuracy audit
- Voltage drop (cable, EV, PV, BESS): the mV/A/m values are single-phase loop values and are now halved per conductor before the 2 or √3 factor. Results were previously about twice the correct drop.
- Earthing (IEEE 80): corrected the Km corner term, n = na·nb, the Lm term for rods, and the BS 7430 plate formula.
- Power factor correction: capacitance is now shown correctly in µF at the system voltage.
- VT sizing: IEC 61869-3 voltage factors and the open-delta winding voltage corrected.
- IEC 60909: the peak current uses method B (1.15·κ) when several sources feed the fault.
- MV cable: trefoil mutual heating for direct burial and the air gap for ducts included in T4.
- NEC: rounding rules for 430.62 and 440.22, the 240.4(D) small-conductor limit, 2000 kcmil at 60 °C, 220.57 EVSE load and the 392.22 mixed-cable tray rule corrected.
- IEEE 43: minimum insulation resistance by winding type.
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